The present invention relates to a control device for a copier or similar image recording apparatus which includes a charger for charging a photoconductive element, a bias voltage source for development, a controller for controllably varying the output of the bias voltage source, and sensor for sensing the trailing edge of a paper.
A problem with a copier, printer, facsimile apparatus or similar range recording apparatus which is implemented by electrophtography is that, when use is made of a paper of relatively small size, image fragments remain untransferred in a non-image area of a photoconductive element which follows the trailing edge of such a paper, resulting in wasteful consumption of toner and an increase in the amount of toner collected. This problem may be eliminated by illuminating and thereby erasing the remaining image fragments in the non-image area based on the size of a paper, as disclosed in Japanese Laid-Open Patent Publication No. 60-6966 by way of example. Such an implementation is extensively used with modern copiers and reported to nearly achieve the above purpose. However, since the illumination scheme needs an exclusive eraser and an exclusive driver, the construction become complicated and the cost is increased. The increase in cost is especially problematic when it comes to a miniature image recording apparatus such as a miniature copier with which a simple and inexpensive construction is prior to the others. While a charger for charging a photoconductive element may be turned off when the trailing edge of a paper is sensed, this kind of scheme cannot be implemented without complicating the construction of a control device as well as the control procedure. Another approach recently proposed is increasing a bias voltage for development timed to the detection of the trailing edge of a paper to thereby reduce toner consumption. Although such an approach may provide a plurality of stable bias voltages as desired, it simply reduces toner consumption necessary to develop an image on a photoconductive element and cannot prevent toner from entering a cleaning unit and increasing the load of a cleaning unit. Especially, under those conditions which intensify the adhesion of toner to a photoconductive element, incomplete cleaning is apt to occur.